Leaching of low-grade copper ores: A case study for 'Kraku Bugaresku-Cementacija' deposits (Eastern Serbia)

Abstract

This paper deals with the investigation of column leaching of low-grade ores from the copper mine Cerovo,
Serbia (the approximate Cu content in the ore ranges from 0.2 – 0.3 % with >10 % copper in the form of oxide minerals). The leaching experiments were performed using sulphuric acid solutions, whereby the kinetics of copper leaching was investigated with respect to acid concentration and solid to liquid ratio. The copper concentration in the leach solution ranged from 0.80 to 1.75 g dm -3 . The total Cu recovery rate ranged from 30 to 56 %, whereas the recovery rate of copper oxide minerals ranged from 67 to 100 %. Furthermore, with increasing the amount of liquid phase, copper recovery increases as well, and copper oxide minerals were completely leached out. Besides copper ions, considerably high ferrous/ferric ion concentrations were achieved in the leach solution. This concentration was sufficiently high for the use of either solvent extraction or ion exchange techniques or both for further treatment of the leach solution.

Key words: low-grade ores; copper minerals; column leaching.

Full text

Journal of Mining and Metallurgy, 52 A (1) (2016) 45 - 56
#Corresponding author: gbogdanovic@tfbor.bg.ac.rs
LEACHING OF LOW-GRADE COPPER ORES: A CASE STUDY FOR „KRAKU
BUGARESKU-CEMENTACIJA” DEPOSITS (EASTERN SERBIA)
Grozdanka D. Bogdanović#, Velizar D. Stanković, Maja S. Trumić,
Dejan V. Antić, Milan Ž. Trumić
University of Belgrade, Technical Faculty in Bor, Vojske Jugoslavije 12, 19210 Bor, Serbia
(Received: October 5, 2016; Accepted: December 14, 2016)
Abstract
This paper deals with the investigation of column leaching of low-grade ores from the copper mine Cerovo,
Serbia (the approximate Cu content in the ore ranges from 0.2 - 0.3 % with >10 % copper in the form of oxide
minerals). The leaching experiments were performed using sulphuric acid solutions, whereby the kinetics of copper
leaching was investigated with respect to acid concentration and solid to liquid ratio. The copper concentration in
the leach solution ranged from 0.80 to 1.75 g dm-3. The total Cu recovery rate ranged from 30 to 56 %, whereas the
recovery rate of copper oxide minerals ranged from 67 to 100 %. Furthermore, with increasing the amount of liquid
phase, copper recovery increases as well, and copper oxide minerals were completely leached out. Besides copper
ions, considerably high ferrous/ferric ion concentrations were achieved in the leach solution. This concentration was
sufficiently high for the use of either solvent extraction or ion exchange techniques or both for further treatment of
the leach solution.
Key words: low-grade ores; copper minerals; column leaching.
1. Introduction
The highest quantities of copper, lead and
zinc in the world are obtained by sulphide ore
treatment. The reserves of high-grade ores
from which the extraction of non-ferrous, rare
and noble metals is technologically and
economically feasible are becoming scarcer
year by year. At the same time, economic
growth requires constantly increasing
production of these metals from ores [1, 2].
Hence, in recent years, greater attention has
been paid to the processes of treatment of raw
materials with low content of these metals
[3, 4].
The increasing demand for copper in the
last few years has been particularly evident
not only in China but also in India, owing to
the rapid industrial development in these
countries. Due to the expected economic
growth in other parts of the world as well (for
instance South America and Africa), the
demand for copper can justifiably be expected
to remain high and continue to grow in the
coming decades [5].
The average grade of copper ores that are
currently mined in the world amounts to
approximately 0.62%, with annual production
of 16 Mt/year [6]. Based on the latest
published results, it is estimated that mineral
resources in the world contain about 1780.9
Mt Cu, with an average copper content being
about 0.49 % [5]. Consequently, a continuing
trend of mining leads to a excavation of lower
grade copper deposits, what can be expected
in the future.
Increasingly, lower-grade deposits are
being exploited in all larger world mines that
J o u r n a l o f
M i n i n g a n d
M e t a l l u r g y

46 G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56
have been operating for over 100 years, such
as Bingham Canyon (USA), El Teniente
(Chile), Mt Lyell (Australia) [7, 8], as well as
the Mining and Smelting Basin Bor (RTB),
Serbia.
At the beginning of the 20th century,
copper mines within the RTB Company
ranked among the highest-grade copper mines
(on average 5 – 6 % Cu in the ore). At the end
of the century, the average Cu content in the
RTB Bor mines fell to less than 0.4 %, which
is illustrated by Fig. 1. Consequently, it is
now ranked among lower-grade copper mines
in the world [9].
Figure 1. The changes in copper content in
the ore with the time of exploitation at the
RTB mines [9]
Oxide copper ore, mixed oxide-sulphide
ores and low-grade copper sulphide ore,
which, for economic reasons, cannot be
enriched by flotation, may be processed by
leaching methods. Agents for leaching copper
can be acid, base, or salt solutions. Of all of
these agents, sulphuric acid has been given the
broadest industrial application in
hydrometallurgy of copper.
The basic copper carbonate minerals,
which are easily leached with the solution of
sulphuric acid are: azurite, malachite and
chrysocolla. Cuprite, tenorite and elemental
copper, which are also found in ore deposits
of copper, can be converted into a soluble
form by leaching, where the chemistry of the
process is simple. Copper carbonates and
oxides, are present mainly in the oxidation
zone - "oxide hats" above the sulphide
deposits.
Sulphide copper minerals chalcocite,
covellite and chalcopyrite, which are mostly
present in sulphide ores of copper, can be
leached only in the presence of oxidants, or
with the help of bacteria from the genus
Acidithiobacillus (formerly Thiobacillus),
which are isolated from mine water.
They were later identified as Acidithiobacillus
ferrooxidans and Acidithiobacillus thiooxidans.
Kinetics of the leaching of the copper
sulphide was significantly slower than the
leaching of carbonates and oxides of copper,
and the mechanism and the stoichiometry of
the process were more complex due to the
participation of oxidants in them. For the
oxidation of sulphides, various oxidizing
agents were used, in addition to oxygen from
the air and ferric - ion was most widely used
on an industrial scale. Ferric ion mostly
occurs in the landfill itself in the form of
Fe2(SO4)3 as the result of decomposition of
pyrite. Therefore, pyrite, which is always
present in the ore deposits of copper, is an
important mineral, as its oxidation supplies
leaching solution with ferric sulphate and
partly sulphuric acid [10, 11].
Mine development and exploitation of
sulphide mineral deposits, as is the case at
RTB Bor, imply the formation of waste
dumps of the so called out-of-balance raw
materials in the vicinity of the mine. Over
time, atmospheric oxygen and bacteria cause
oxidation of pyrite and other sulphide
minerals. As a result of weathering, the
products of oxidation are dissolved and
leached in the form of acid mine drainages
(AMDs), whose influence on the environment
is extremely harmful due to a high content of
heavy metal ions and sulphuric acid [12-15].

G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56 47
Oxidation reactions and leaching of copper
minerals and pyrite from low-grade copper
ores and mining waste (waste rock,
overburden, oxidized portions of the ore
body) proceed according to the following
stoichiometric equations shown in Table 1
[16].
Dump, heap and in-situ leaching are the
most common hydrometallurgical methods for
copper recovery from these raw materials on
an industrial scale [16-18]. A considerable
amount of copper is recovered using these
methods, which reduces uncontrollable
pollution of the environment with heavy metal
ions and acid occurring as a result of the
natural leaching processes represented by the
equations in Table 1. Currently, leaching in
combination with the solvent extraction and
electrolysis account for 20 % of the total
amount of copper produced in the world
[19, 20]. These methods are most widely used
in the USA and Chile.
Table 1. Reactions for leaching copper minerals and pyrite
Minerals Reaction(s)
Copper sulphides
Chalcocite
Cu2S +1/2O2 + H2SO4→CuS + CuSO4 + H2O (1)
Cu2S +Fe2 (SO4)3→ CuS + CuSO4 + 2FeSO4 (2)
Covellite
CuS + 2O2→ CuSO4 (3)
CuS +Fe2(SO4)3→ CuSO4 + 2FeSO4 + S (4)
Chalcopyrite
CuFeS2 + O2 + 2H2SO4→CuSO4 + FeSO4 + 2S +2H2O (5)
CuFeS2 +2 Fe2(SO4)3→CuSO4 + FeSO4 + 2S + 2H2O (6)
Copper carbonates, oxides and silicates:
Malachite
Cu2 (OH)2CO3+ 2H2SO4+ 2CuSO4 + 3H2O+ CO2 (7)
Azurite
Cu3(OH)2(CO3)2+ 3H2SO4→ 3CuSO4 + 4H2O+ 2CO2 (8)
Cuprite
Cu2O +1/2O2 + 2H2SO4→2CuSO4 +2H2O (9)
Chrysocolla
CuSiO3+2H2O + H2SO4→CuSO4 + SiO2+3H2O (10)
Pyrite
FeS2 + 3.5 O2 + H2O → FeSO4 + H2SO4 (11)
2 FeSO4+ H2SO4 + 0.5 O2 → Fe2(SO4)3 + H2O (12)
FeS2 + 7Fe2(SO4)3 + 8H2O → 15 FeSO4 + 8H2SO4 (13)
The potential raw material for obtaining
copper within the RTB Bor include oxide and
mixed oxide-sulphide ores at the copper
deposit "Kraku Bugaresku -Cementacija".
This deposit, in the calculation of reserves
in the contour of boundary contents of 0.2 %
Cu, is consisted of four ore bodies (C1, C2,
C3 and C4), which are similar in generic

48 G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56
origin, but with some differences in the
composition of the copper mineralization.
From the surface toward the depth, there is a
vertical zoning, where we can recognise: the
oxidation zone, the zone of secondary
sulphide enrichment or, so called cementation
zone, transient and primary zone, as is
illustrated in Table 2 [21, 22].
Table 2. Copper content in the ore bodies "Kraku Bugaresku - Cementacija"
ORE SAMPLE
TOTAL COPPER
OXIDE COPPER
SULPHIDE COPPER
Conc. %
Fraction %
Conc. %
Fraction %
Conc. %
Fraction %
Cementation zone C2
0.32
100
0.13
40.62
0.19
59.38
Transient zone C2
0.23
100
0.04
17.39
0.19
82.61
Cementation zone C3
0.31
100
0.07
22.26
0.24
77.73
Transient zone C3
0. 33
100
0.024
7.27
0.31
92.73
C4 Average [1]
0.27
100
0.03
11.20
0.24
88.80
*Sample from C1
0.18
100
0.08
44.40
0.102
55.60
* Sample taken from an edge at the open pit Cerovo reach with oxide copper minerals
Low average copper content and increased
participation of oxide copper minerals in these
ore bodies, leads to serious technological
problems in mineral processing plant, namely
to reduction of copper in the flotation
concentration (about 60 % on average). This
leads to large copper losses. Therefore, studies
were conducted to obtain copper from these
raw materials with the process of leaching of
the present minerals and subsequent
extraction of copper from the leach solution.
This paper describes the influence of acid
concentration and influence of solid/liquid
ratio on copper leaching rate from the ore
bodies Cerovo-Cementacija 2 (C2).
2. Experimental
2.1. Material
The leaching experiments were conducted
using two representative ore samples taken
from the Cerovo-Cementacija 2 ore body with
various copper oxide content. The samples
originate from the drilling cores taken from
different depths of the cementation and
transient zones. Subsequent to drying,
homogenization and reduction of samples
they were characterized based on particle
size analysis, chemical and mineralogical
composition.
The particle size distribution is shown in
Fig. 2.
0,01 0,1 1 10
10
20
30
40
50
60
70
80
90
100
Participation,%
Grain size, (mm)
Cementation zone C2
Transient zone C2
Figure 2. Grain size distribution of the ore
sample
The results of chemical analysis of the
samples are shown in Table 3.
It can be concluded that the analysed
samples represent a low-grade copper ore with
a high content of non-sulphide minerals. As
indicated by these data, the percentage of
copper oxide compared to the total amount of
copper ranged from 40.6 % (cementation
zone) to 17.3 % (transient zone).

G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56 49
Table 3. Chemical analysis of the ore samples
Component
Cu-
total
Cu-
oxide
Cu-
sulfide
S
SiO2
Fe
Al2O3
CaO
MgO
Ni
Zn
Mn
Cementation
zone C2,%
0.32
0.13
0.19
2.66
63.14
3.37
19.42
0.47
2.11
0.007
0.016
0.012
Transient
zone C2,%
0.23
0.04
0.19
1.95
60.64
4.14
18.47
0.66
2.,84
<0.007
0.010
0.012
Mineralogical analysis and X-ray
diffraction revealed that the most abundant
sulphide mineral was pyrite, and of copper
minerals, the most abundant were chalcocite
and chalcopyrite. Copper is mostly present in
the form of cuprite, malachite and azurite. The
results of qualitative mineralogical analyses
indicated the presence of other iron minerals
apart from pyrite such as: magnetite, goethite,
rutile, limonite as well as smaller amounts
sphalerite, molybdenite and galenite in quartz-
sulphide wires. Among the gangue minerals
the most abundant is quartz.
2.2. Column leaching experiments
Leaching experiments were carried out in
PVC columns, 110 mm in diameter and 1000
mm in height. At the bottom of each column
there was a perforated plate serving as a bed
carrier over which filter paper was placed to
prevent small solid-phase fractions from
passing through. Eight kilograms of ore, grain
size range - 5 + 0 mm, was put into each
column. Over the ore, a bed of silica sand was
placed 1cm in height in order for sulphuric
acid solution to be more evenly distributed
over the whole cross section of the column.
The leaching agent used in the experiment
was a 0.01 M and 0.1 M sulphuric acid
solution. Above each column, there was a
reservoir with sulphuric acid solution (V=10
dm3) which gravitationally flows out into the
column. Under the columns, reservoirs were
placed for the collection of the pregnant leach
solution. At definite intervals, the samples of
leach solution were taken for analysis and pH
measurements. After pH adjustment to the
initial value, the solutions were re-circulated
through the column. The pH value adjustment
was performed using a sulphuric acid solution
of a known concentration. A layer of the
leaching agent was kept constant to ensure a
constant flow. The flow was controlled by
taps at the bottom of each column and was
kept constant throughout the experiment. The
flow rate was about 12 cm3/min and the
leaching experiments lasted 30 days.
Copper and iron concentration in the leach
solutions was determined using a UV/VIS
spectrophotometer Rayleigh UV 9200 and
atomic absorption spectroscopy (AAS). The
pH values of the solutions were periodically
changed using the JENCO 6250 pH meter.
3. Results and discussion
3.1. Influence of sulphuric acid
concentration
The influence of sulphuric acid concentration
on the leaching of copper and iron was
investigated by leaching ore samples, at a
solid to liquid ratio of 1:1, class of size (- 5 +
0) mm. The initial H2SO4 concentrations in
the leach solution were 0.01M and 0.1M and
were kept at that level by periodic addition of
sulphuric acid. The obtained results of the
leaching are presented in Fig. 3.
Curves in Fig. 3a show an increase the
copper and iron ions with time. During the
leaching process of the ore from the
cementation zone after a period of 28 days,
the concentration of copper in the leach
solution was 1.75 g dm-3.

50 G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56
a)
b)
Figure 3. Change of concentration copper
and iron ions concentrations with time during
copper ore leaching with 0.01 M H2SO4;
Particles size: -5 + 0 mm:
a) cementation zone, b) transient zone
The concentration of iron ions in the leach
solution was significantly lower than the
concentration of copper ions, with the amount
of 0.67 g dm-3.
Figure 3b shows similar behaviour like
during the leaching process of the ore from
cementation zone of the ore body. Obtained
kinetic curves of the leaching confirm that,
but the copper concentration in the solution
was half in the case of the transition zone
(~0.80 g dm-3 Cu), which is due to
mineralogical composition of the ore (lower
copper content in the form of oxide minerals).
The concentration of iron in the solution was
about 0.5 g dm-3.
Concurrently with leaching of oxide
minerals, there was a process of oxidation of
sulphide copper minerals thanks to the Fe3+
ions, which are present as the result of the
leaching of iron oxides. In extended leaching
experiments, molecular oxygen dissolved in
the leach solution can have the role of an
oxidant, oxidizing Fe2+ to Fe3+. The generated
ferric ion will act as an oxidant for the
subsequent oxidation of sulphide copper
minerals.
Under natural conditions, the presence of
certain indigenous species of bacteria has a
favourable effect on these processes,
oxidizing Fe2+ to Fe3+, which can affect the
rate of leaching of copper sulphide minerals.
This practically means that the leaching of
copper in the dump, or heap takes a very long
time - even years, depending on the size of the
dump, or heap, copper content in it and access
to agents for leaching copper minerals [4, 16].
Figure 4 shows the influence of the
concentration of acids on the recovery of
copper.
During the leaching of the ore with
sulphuric acid concentration of 0.1 and 0.01
M H2SO4 , leaching degree of total copper
ranged from about 27 to about 55 %,
respectively. Given that the degree of leaching
of total copper was larger than the amount of
oxide copper present in the sample (41 % ), it
can be concluded that an oxidation reaction
occurs between copper sulphide minerals,
followed by dissolution of so formed oxides.
The copper content in the leach solution
has reached, after 5 days about 1 g dm3 (Fig.
3a). At the very beginning of the process (first
two days), around 67 % of copper oxide was
leached, after and after 10 days of leaching,
leaching degree was over 90 %.
Figures 3 and 4 show that the leaching
process of copper minerals takes place with
very different rates. Significant high rate was
achieved of the process during the first 2-5
days, to be reduced 1-2 order of magnitude,

G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56 51
depending on the conditions of the process.
During the testing of the sample leached with
the solution 0.01 M H2SO4 any significant
acid consumption was not observed.
0 5 10 15 20 25 30 35
0
10
20
30
40
50
60
70
80
90
100
Recovery,%
Time, days
Cementation zone
0.1 M H2SO4
0.01 M H2SO4
a)
0 5 10 15 20 25 30
0
10
20
30
40
50
60
70
80
90
100
Recovery,%
Time, days
Transient zone
0.1 M H2SO4
0.01 M H2SO4
b)
Figure 4. Effect of sulphuric acid
concentration on copper recovery (S:L=1:1):
a) cementation zone, b) transient zone.
3.2. pH behaviour during column
leaching
The change in the pH value of the pregnant
leach solution with time is shown in Fig. 5a
and 5b.
0 5 10 15 20 25 30
0
1
2
3
4
5
pH
Time,days
Cementation zone
0.1 M H2SO4
0.01 M H2SO4
a)
0 5 10 15 20 25 30
0,0
1,0
2,0
3,0
4,0
5,0
pH
Time, days
Transiente zone
0.01 M H2SO4
b)
Figure 5. Change in the pH value of the
leaching solution vs. time:
a) cementation zone, b) transient zone.
It can be observed that the pH value
increases in the initial period of the leaching
process (up to two days), after which it
slightly decreases with time. During the
leaching process, sulphuric acid is consumed
due to wanted reactions with copper minerals,
but also due to unwanted reactions with
oxides and carbonates of alkaline earth

52 G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56
metals, which is manifested by an increase in
the pH value of the leach solution by almost
one unit, that is, the decrease in H+
concentration in the leach solution.
In order to provide sulphuric acid
throughout the process and maintain constant
acidity of the leach solution, the pH was
adjusted to 2.0 by adding sulphuric acid with
each recirculation of the leach solution. The
greatest amount of acid is consumed in
leaching copper oxides (Eqs. (7)–(10). A
considerable amount is of sulphuric acid is
consumed in leaching other oxide and
carbonate minerals present in the ore, whereas
a slight amount is consumed in leaching
secondary copper sulphide minerals (Eqs. (1)-
(6)). However, a part of acid is generated
during the reaction of pyrite leaching (Eqs.
(11) and (13)), which is indicated by the
amount of iron ions in the final leach solution.
Pyrite oxidation is carried out in several
stages, including the oxidation of pyrite,
iron (III) hydrolysis and formation and
precipitation of secondary products. These
products consist of iron (III) oxide
/ oxyhydroxides (i.e. geothite-FeO(OH) or
α-FeOOH; ferrihydrite Fe5HO8∙4H2O
or Fe2O3∙9H2O) and iron (III) sulphate
(i.e. schwertmannite Fe8O8(OH)6SO4 and
Fe16O16(OH)10(SO4)3) as well as from much
more stable jarosite KFe3(SO4)2(OH)6. The
hydrolysis and precipitation of iron hydroxide
(reaction 14) and to a lesser extent of jarosite
(reaction 15), will produce the most of acid
during the oxidation of pyrite [23].
Fe3+ + 3H2O ↔ Fe(OH)3 +3H+ (14)
Fe3+ + 2H2O ↔ FeOOH(s) +3H+ (15)
3.3. Effect of solid to liquid ratio
The effect of solid/liquid ratio (S:L) was
investigated by leaching the ore samples with
a 0.01M H2SO4 solution at a solid to liquid
ratio of 1:1 and 1:2. The obtained results are
shown in Fig. 6 and Fig. 7.
a)
0 5 10 15 20 25 30 35
0
100
200
300
400
500
600
700
800
900
1000
Concentration,mg dm-3
Time,days
Transient zone
0.01 M H2SO4
Č:T=1:1
Č:T=1:2
b)
Figure 6. Copper concentration in the leach
solution vs. time at various solid to liquid
ratios: a) cementation zone, b) transient zone.
Fig. 6 and Fig. 7 show that, except for the
first two days, when there was a sudden jump
in the concentration of copper ions in the
leach solution, the process takes place at
almost a constant rate in case of S:L=1:1,
while the copper concentration remains
almost constant for S:L=1:2 and for the
leaching process time.
0 5 10 15 20 25 30 35
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Concentration, mg dm-3
Time, days
Cementation zone
0.01 M H2SO4
Č:T=1:1
Č:T=1:2

G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56 53
0 5 10 15 20 25
0
10
20
30
40
50
60
70
80
90
100
Recovery,%
Time, days
Cementation zone
0.01 M H2SO4
Č:T=1:1
Č:T=1:2
a)
0 5 10 15 20 25 30 35
0
10
20
30
40
50
60
70
80
90
100
Recovery, %
Time, days
Transient zone
0.01 M H2SO4
Č:T=1:1
Č:T=1:2
b)
Figure 7. Effect of solid to liquid ratio on
copper and iron recovery rates in leaching
with 0.01 M H2SO4: a) cementation zone, b)
transient zone.
With the increasing proportion of the
liquid phase, i.e. leaching agent in the
suspension, there was an increase in the
degree of leaching of total amount of copper,
but also a decrease of the concentration of
copper in leach solutions. During the leaching
with a solution concentration of 0.01 M
H2SO4 (S:L = 1:2), after 7 days about 50 % of
the total copper was leached.
The concentration of copper in the leach
solution was about 0.8 g dm-3 and kept this
value through the whole process. After 30
days of leaching a concentration of copper in
the solution was about 0.9 g dm-3, which was
two times lesser compared to the leach
solution at a ratio S:L=1:1. Total copper
leaching degree, after 30 days of leaching was
about 56 %. Changing ratio S:L did not
significantly affect the leaching of oxide
copper, because in both cases, almost all the
copper oxide was converted into ion form,
which can be determined on the basis of its
participation in the raw material.
Fig. 6b, has a similar shape regardless of
the experimental conditions, that is, leaching
of the ore from the transition zone occurs in
two stages, as in the previous case.
During the leaching with 0.01 M H2SO4
(S:L=1:2) for a period of 2 days, leaching
solution concentration of about 0.3 g dm-3 was
obtained, where about 30 % of the total
copper was leached. After 30 days of
leaching, copper concentration in the solution
was about 0.46 g dm-3, where a degree of
leaching of total copper was about 40 %, as
seen in Fig. 6b and Fig.7b. During the
leaching of the ore at ratio S:L=1:1, the
concentration of copper in solution was
almost twice as high, so that after 29 days of
leaching copper concentration was 0.68 g
dm-3, where a degree of leaching of total
copper was about 30 %.
These results are in agreement with the
kinetics of acid leaching of low-grade
sulphide-oxide ores under atmospheric
conditions. It has been found that the copper
recovery rate in heap leaching of sulphide
minerals usually increases rapidly in the initial
stage of the leaching process, with 50 - 60 %
of the metal being leached out in the first few
months. Subsequently, the leaching process
slows down and proceeds at a constant
dissolution rate, during which 80 - 90 % of the
metal is leached out in the next 12 to 24

54 G. Bogdanovic et al. / JMM 52 A (1) (2016) 45 - 56
months [4]. In leaching copper oxide minerals
or mixed sulphide-oxide ores, more than 90%
of copper is commonly leached out in the first
30 days.
In heap leaching of primary copper
sulphides, the achieved recovery rates are
60-70 % in 1-2 years, subsequent to which
leaching stops as not being technologically
and economically feasible due to slow
leaching rates [24].
4. Conclusions
Based on the obtained it can be concluded
that it is a low-grade copper ore with a high
content of non-sulphide minerals (copper
oxide content > 15 %). It can be noted that
there is more iron in the transition zone
compared to the cementation zone.
Based on the shape of curves concentration
– time, the leaching takes place in two stages.
In the first stage, which lasts 2 to 5 days, the
concentration of copper ions in the leach
solution was going rapidly with time up. After
the first stage, leaching process rate decreases
significantly for the rest time of leaching.
High rate of the leaching process in the first
period was the result of easily available oxide
copper.
Due to the recirculation of leach solution,
the copper concentration in the final solution,
after ending the experiment (time interval
about one month), was in a range from 0.8
to 1.8 g dm-3. The concentration of iron ions
was in the range values - from 0.5 to
0.7 g dm-3.
Based on the collected results it can be
noted that, after a certain time of leaching,
leach solutions with significant concentrations
of copper (about 1 g dm-3) are obtained, which
could be further treated with SX-EW process,
or a similar procedure.
The total Cu recovery rate during the
leaching period of about 30 days ranged from
30 to 56%, implying that, in addition to
complete leaching of copper oxide, it leads to
the oxidation of sulphide minerals, either due
to the presence of ferric ions and oxygen
dissolved in the solution.
5. Acknowledgments
This research is supported by the Ministry
of Education, Science and Technological
Development, Government of the Republic of
Serbia within the framework of the Projects
OI 172 031 and TR 33 007. The authors are
gratefully acknowledged.
A part of this study was presented at the
48th International October Conference on
Mining and Metallurgy, University of
Belgrade, Technical faculty in Bor, Bor, on
28th September to 01st October 2016.
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Journal of Mining and Metallurgy, 52 A (1) (2016) 59 - 63
#Kontakt adresa autora: gbogdanovic@tfbor.bg.ac.rs
LUŽENJE RUDA BAKRA SA NISKIM SADRŽAJEM: STUDIJA SLUČAJA ZA
LEŽIŠTE „KRAKU BUGARESKU-CEMENTACIJA” (ISTOČNA SRBIJA)
Grozdanka D. Bogdanović#, Velizar D. Stanković, Maja S. Trumić,
Dejan V. Antić, Milan Ž. Trumić
Univerzitet u Beogradu, Tehnički fakultet u Boru, Vojske Jugoslavije 12, 19210 Bor, Srbija
(Primljen: 5. Oktobar, 2016.; Prihvaćen: 14. Decembar, 2016.)
Izvod
Ovaj rad se bavi istraživanjem luženja u koloni ruda sa niskim sadržajem bakra iz rudnika Cerovo, Srbija
(približni sadržaj Cu u rudi varira u opsegu 0.2 - 0.3 % sa >10 % bakra u formi oksidnih minerala). Eksperimenti
luženja izvedeni su primenom rastvora sumporne kiseline, pri čemu je konetika luženja ispitivana uzimajući u obzir
koncentraciju kiseline i odnos čvrste prema tečnoj fazi. Koncentracija bakra u lužnom rastvoru varirala je od 0.80 do
1.75 g dm-3. Ukupno iskorišćenje Cu variralo je od 30 do 56 % pri čemu je iskorišćenje oksidnih minerala bakra bilo
u rasponu od 67 do 100 %. Dodatno, sa povećanjem količine tečne faze raste iskorišćenje bakra, a oksidni minerali
bakra su u potpunosti izluženi. Pored jona bakra postignute su i značajne koncentracije feritnih jona u lužnom
rastvoru. Ove koncentracije su bile dovoljno visoke za primenu solventne ekstrakcije ili tehnika jonske izmene ili
oboje za dalji tretman lužnog rastvora.
Ključne reči: siromašne rude; minerali bakra; luženje u koloni.
J o u r n a l o f
M i n i n g a n d
M e t a l l u r g y